Lakhmir Singh & Manjit Kaur Test: Motion - Class 9 MCQ

Vector Quantity

• Direction: A vector quantity has a specific direction in space. This means that not only does it have a magnitude, but it also has a specific orientation or direction in which it is pointing.
• Magnitude: In addition to having a direction, a vector quantity also has a magnitude. This magnitude represents the size or strength of the vector, indicating how much of the quantity is present.
• Both Magnitude and Direction: Therefore, a vector quantity possesses both magnitude and direction, distinguishing it from scalar quantities which only have magnitude. This dual nature of vectors allows for a more detailed description of physical quantities.

Topic in NCERT: SPEED WITH DIRECTION
Line in NCERT: "The quantity that specifies both these aspects is called velocity."

Odometer of automobiles records distance travelled: The primary function of an odometer in automobiles is to measure and display the total distance the vehicle has traveled since it was first put into use. This distance is usually displayed in kilometers or miles depending on the unit system used in the region.

Topic in NCERT: Example 7.2

Line in NCERT: "The odometer of a car reads 2000 km at the start of a trip and 2400 km at the end of the trip."

Speedometer Measurement
- Instantaneous Speed: The speedometer of a car measures the instantaneous speed at any given moment.
- It provides a real-time reading of how fast the car is moving at that particular moment.
- This measurement is important for drivers to ensure they are following speed limits and driving safely.
- It helps drivers make adjustments to their speed based on road conditions, traffic, and other factors.

If the displacement-time graph of a particle is parallel to the time axis, this means that the displacement remains constant over time. In other words, there is no change in displacement as time progresses.

Since velocity is defined as the rate of change of displacement with respect to time, and there is no change in displacement, the velocity of the particle is zero.

Topic in NCERT: VELOCITY-TIME GRAPHS

Line in NCERT: "if the object moves at uniform velocity, the height of its velocity-time graph will not change with time."

Explanation:

Displacement is the straightest shot (shortest distance) between start and end. Distance is the total path taken. Imagine going for a walk around a block - the displacement is the length of one side, while the distance is the entire walk. The numerical ratio of displacement to distance is calculated as displacement divided by distance. So the ratio:

• Can be 1 (straight path)
• Is less than 1 (curved path or going back and forth)
• Never more than 1

Therefore, the answer is D: equal to or less than 1.

Topic in NCERT: MOTION ALONG A STRAIGHT LINE

Line in NCERT: "The magnitude of displacement (35 km) is not equal to the path length (85 km)."

The correct answer is C: zero displacement.

Explanation: 

• Displacement is the straight line distance between the starting and ending points of an object's motion.
• In this scenario, the body starts at A, goes to B, and then returns to A. Even though the body travels a certain distance (twice the distance between A and B), it ends up back at its starting point (A).
• Since displacement considers the net change in position, and the body ends at the same point it started, the displacement is zero.

Topic in NCERT: Distance and Displacement

Line in NCERT: "the final position coincides with the initial position, and therefore, the displacement is zero."

Option B is correct. 

In a distance-time graph, the slope or gradient. The greater the gradient, the greater the rate of change. of the line is equal to the speed of the object. The steeper the line (and the greater the gradient) the faster the object is moving.

Topic in NCERT: Graphical Representation of Motion

Line in NCERT: "Thus, the graph shown in Fig. 7.4 indicates that a steep slope represents faster motion."

Option B is correct. Car B is the slowest
-Car B covers the least distance in the same amount of time compared to the other cars, making it the slowest among the four.

Displacement = Area of ΔABC
a = 1/2 x 5 x 20 = 50 m.

Acceleration is the measure of how fast the velocity changes. Velocity is a vector quantity and a change in velocity is due to  change in magnitude or change in direction or both. Here,  the boy is moving with constant speed but velocity changes and hence is supposed to be in accelerated motion.